Maintenance
The correct major overhaul of air-cooled diesel engines
The determination of the major overhaul time for air-cooled diesel engines
The determination of the major overhaul time for diesel engines mainly depends on the changes in their power performance, economy and smoke and dust in practical applications, such as power decline, increased fuel consumption, oil burning, oil pressure drop, crankcase air leakage, and even obvious abnormal noises. The major overhaul interval for air-cooled diesel engines is generally 8,000 to 10,000 working hours.
Preparations before major overhauls of diesel engines
2.1 Establish a major engine overhaul file
Keep a record of the technical condition of the engine before major overhauls, report it to the competent department for approval, and also record the model, factory serial number, production date and the type of diesel engine it is matched with.
2.2 Preparation of tools for disassembly and assembly
(1) Conventional tools such as wrenches and sockets commonly used in maintenance.
(2) Special tools:
a flip bracket that matches the engine.
Angle indicator for b fastening.
Special tool for adjusting c valves.
Installation tools for D-piston and piston rings.
e filter element wrenches, etc.
(3) Material preparation
Mainly prepare some commonly used gaskets and sealants. The sealants we commonly use are 703 silicone rubber, Huatian 586 sealant and GY series anaerobic sealant.
3. Inspection after disassembly
3.1 Inspection of the crankshaft journal and bearing bush
The detection positions are shown in Figure 1. Measure the data in the A-A and B-B directions at positions 1 and 2 and make good records.
The allowable wear limit size for the main journal of the crankshaft and the connecting rod journal is 0.3mm. Grinding can be carried out when the wear limit is exceeded. The commonly used grinding grades at present are determined by the size of the thickened bearing bush (divided into three levels :0.25mm, 0.5mm, 0.75mm). Simultaneously measure the out-of-roundness in both A-A and B-B directions, which shall not exceed 0.05mm.
Taking the main journal at both ends as the reference, measure the radial runout of the intermediate journal, which should be less than 0.1mm.
The axial play of the crankshaft should not exceed 0.4mm. Taking F6L912 and 913 as examples, the axial play of the crankshaft is 0.15 -0.314. After major overhauls, this requirement must be guaranteed (the width of the thrust main bearing cover is, and the out-of-roundness of the bearing bush should not exceed 0.05mm when tested under the standard preload force F=270 n.m).
3.2 Inspection of Cylinder Heads
Carefully inspect the cylinder head for any cracks. Check the descent of the valve cover. Its limit size is 5.8mm. If it is too large, it will affect the compression ratio. To check the sealing condition between the valve seat ring and the valve, generally, the width of the valve imprint should be between 0.3 and 0.5mm, and it should be straight and uniform. The valve seat ring is an interference fit in the seat hole on the cylinder head, with an interference amount of 0.115-0.160. Installation and disassembly are often heated to 220℃. Deutz Company specially provides users with dedicated drill bits and tools.
3.3 Inspection of Cylinder Liners and piston Rings
The detection positions of the cylinder liner and piston ring are shown in Figure 2. Measure the positions 1,2,3, and 4 in both A-A and B-B directions and make records.
When the cylinder liner is severely worn, when the first gas ring reaches the highest position of the cylinder liner, a step can be clearly felt with a fingernail. The limit value should be 0.2mm, at which point the honing marks on the cylinder barrel no longer exist. At present, the widely used method is to replace all the standard cylinder liners. At this time, the standard pistons and piston rings need to be replaced for assembly.
3.4 Check the fit between the intake and exhaust valve guides and the intake and exhaust valves
The limit value of the fit clearance between the valve guide and the valve is approximately 0.3 to 0.5mm. If this limit is exceeded, a new valve guide or valve should be replaced. The valve guide should be enlarged, as shown in the following table (taking F6L912 and 913 as examples). When assembling, all the valve oil seals and valve lock plates should be replaced simultaneously. Check whether the valve springs are rusted or cracked. And measure its free length.
The valve guide dimensions of F6L912 and 913 engines
3.5 Inspection of fuel injection pumps and injectors
1) The fuel injection pump is calibrated in accordance with the diesel engine product manual on the test bench and adjusted to the best condition.
2) The fuel injection pressure and spray condition of the fuel injector can be inspected on the test bench. The fuel injection pressure of the new fuel injector pair is 18.0+0.5Mpa, and that of the in-use fuel injector pair is 17.5+0.5MPa.
3.6 Inspection of the rotating device of the valve train
The rotating device should be flexible without any jamming, and the wear of each component should not exceed the limit values specified in the specifications.
3.7 All sealing elements such as cylinder liners, crankshaft oil seals, and intake and exhaust branch pipe gaskets should be updated during assembly.
3.8 Replace the filter elements of the new diesel and engine oil filters and clean the air filter.
3.9 Adjustment of each drive belt
The manually adjusted drive belts must have their downward pressure adjusted as required, especially for newly replaced toothed belts, which should be readjusted after running for 30 to 50 seconds. The method is to press down 10 to 15mm with the thumb when applying force.
Major overhauls of cold diesel engines should be carried out carefully. It is best to replace the bolts of some high-strength and key parts with new ones and conduct inspections after running for a period of time. After a major overhaul of a diesel engine, if the conditions for test run are met, cold running-in should be carried out on a test bench to make operational adjustments, measure its power, torque, fuel consumption and smoke exhaust, and meet the national standard requirements. During use, special attention should be paid to reducing the load during the running-in period. The engine oil and filter element should be replaced within the specified time, and the air filter should be cleaned frequently to keep the air-cooled diesel engine in the best working condition.
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